A fossil fuel power plant is a system that burns fossil fuel such as coal, natural gas or petroleum to produce electricity. Most power plant systems convert fossil fuel energy to mechanical or electric energy by burning fuel (coal, natural gas or petroleum) in a vessel (e.g., a boiler) and circulating a working fluid such as water through the boiler. In the case of water as the working fluid, the fuel converts the water to high temperature and pressure steam and the steam in turn is used to do work in the form of rotating a turbine shaft. The steam does work as it expands through the turbine. The rotation of the shaft is then converted to electrical energy from a generator. From the turbine, the working fluid is transferred to a condenser where it is condensed by, for example, a heat exchange process. The working fluid (condensate) is then cycled back into the heating vessel.
The main purposes of the condenser are to condense the working fluid (e.g., steam) from the turbine for reuse in the cycle and to maximize turbine efficiency by maintaining proper vacuum. One type of condenser used in power plant systems is a shell and tube heat exchanger. As heat exchangers, these condensers convert the working fluid (e.g., steam) from a gaseous to liquid state by a cooling medium (e.g., water) at atmospheric pressure or below atmospheric pressure. The working fluid (e.g., steam) from the turbine flows on the shell side of the condenser, while the cooling medium flows in the tube side. Most of the heat liberated due to condensation of the working fluid is carried away by the cooling medium (e.g., water). The condensed working fluid (condensate) is collected in the bottom of the condenser (in a hot well) and then pumped back to the heating vessel (e.g., boiler) to repeat the cycle.
A large volume of cooling medium (e.g., water) must be circulated through the tubes of the condenser to absorb the heat from the working fluid (e.g., steam). As the steam cools and condenses, the temperature of the cooling water rises. The waste heat generated at the condenser is released to the atmosphere through a cooling tower associated with the condenser.
Water-based cooling systems fall in either once-through or closed-loop designs. Once-through cooling systems withdraw a large volume of water from river, lake, estuary or ocean. The water is pumped through a condenser in a single pass and returned to the same or nearby water body.
Closed-loop cooling systems receive their cooling water from a cooling tower and basin, cooling pond or cooling lake that is typically associated with a river, lake, estuary or ocean as a water source. Because evaporation in plant cooling towers removes cooling water from the evaporated system, regular additions of “make-up” cooling water are needed from the source. Make-up volumes are much lower than daily once-through volumes and may range from hundreds of thousands to millions of gallons per day.
Recently, to meet cooling water demands, particularly in closed-cycle cooling systems, the power plant industry has looked to reclaimed water as an additional source. Reclaimed water includes domestic and industrial wastewaters, such as water from oil and gas wells, mine pool waters, produced water from carbon dioxide storage in saline formations, and ash pond basins.
Corrosion and the build up of scale in a condenser caused by the cooling medium (e.g., water) is a concern.